Originally Posted by
Endus
There's a reason nobody does this in the real world. When you finish early, you've now set a new expectation that you will always be able to finish that early. You said it would take 7 hours, you were done in 3. When you get asked to do it again, and say "It'll take 7 hours", the first thing your client/boss says is "last time it only took you 3 hours, what's the deal?"
Now they're thinking you're just lying to them, making up numbers to make yourself falsely seem better. And, if you fail to meet that new 3 hour deadline you set, they'll think it's just because you called them on it so you're delaying it artificially, wasting their time on purpose.
In the real world, you say "Assuming everything goes right, X hours". And then when something doesn't go right, you've got a clear reason for the delay. Lying to your boss/customers to defraud them into thinking you're better than you are works fine, up until you keep setting that long deadline and beating it (why does he keep saying it'll take longer?) or they get a second quote from someone who gives them an accurate timeline, the time you'd have finished it in yourself if you'd been honest the first time around.